Means for prventing reverse drive through a hydrostatic transmission

ABSTRACT

A means for automatically preventing a motor, which is hydraulically driven by a pump and mechanically drives an inertial load from a pumping action of the motor caused by being driven by said inertial load, comprising blocking a reverse power transmission. The blocking may be done by brake disc fixed to a transmission shaft or by declutching a pair of clutching members arranged across the shaft. The automatic actuation of the blocking action may be either mechanically or electrically effected.

ilniie @fiates ate Ninorniya l Feb. 1, 1972 5 1 M NSEQR PRIEYENIL REVERBREE THROUGH A HYDROSTATIQ TRANSMHSSIQN [72] Inventor: Kenji Ninomiya,Kawasaki-sin, Japan [73] Assignee: Kabushiki Kaisha Komatsu Seisakusho(Komatsu Ltd), Akasaka, Tokyo, Japan [22] Filed: Nov. 6, 1969 211 App].No.: 874,644

[30] Foreign Application Priority Data Dec. 27, 1968 Japan ..43/95521Dec. 27, 1968 Japan ..43/95522 [52] US. Cl ..l92/4 B, 192/8, 192/357,

192/358, 60/53 A, 188/370 [51] int. Cl. ..F16d 67/00, 860k 29/00, 860k21/00 [58] Field oi Search ..l92/4 B, 8, 3.34; 60/53 A [56] ReferencesCited UNITED STATES PATENTS 2,073,357 3/19317 wemp ,192/33820 2,885,0435/1959 2,925, l 57 2/ l 960 2,945,572 7/ l 960 2,500,32l 3/19503,390,523 7/1968 3,507,371 4/1970 Richards et al. 192/334 X PrimaryExaminer-Benjamin W. Wyche AnorneySteinberg & Blake 57] ABSTRACT A meansfor automatically preventing a motor, which is hydraulically driven by apump and mechanically drives an inertial load from a pumping action ofthe motor caused by being driven by said inertial load, comprisingblocking a reverse power transmission. The blocking may be done by brakedisc fixed to a transmission shaft or by declutching a pair of clutchingmembers arranged across the shaft. The automatic actuation of theblocking action may be either mechanically or electrically effected.

3 Claims, 4 Drawing Figures PATENTED EB 1 i972 SHEET 2 0F 2 MEANS FORPRVENTING REVERSE DRHVE THROUGH A HYDROSTATIC TRANSMHSSION Thisinvention relates to a means for automatically preventing a motor, whichis hydraulically driven by a pump and mechanically drives an inertialload, from pumping caused by being driven by the inertial load.

The pump and the motor in the hydraulic power transmission system are,in general, characterized in that it is possible to gradually vary thereduction gear ratio thereof, so that either the pump or the motor orboth the pump and motor are of variable capacity. In such a hydraulicpower transmission, when the load is rotated at a high speed, a largecapacity of the pump and a small capacity of the motor are required,and, during at a low speed on the load side, a small capacity of thepump and a large capacity of the motor are required. Under thesecircumstances, when the speed of the motor is suddenly lowered, thehydraulic motor tends to be reversely driven by the inertial load so asto rotate the large capacity motor at a high speed as a pump, andtending to rotate the small capacity pump at a higher speed. lnaddition, for example, when a car driven by a hydraulic motor goes downa down grade in the state of a small capacity of the pump and a largecapacity of the motor, the motor, and therefore, the pump also, aredriven by the inertial load due to an external force, similarly to theabove situation.

When the hydraulic pump is reversely driven up to an unusually highspeed, it is inevitable that various significant troubles such asseizure at the sliding contact surface of the pump, a damage of theprime mover, and the like will occur and the durability of the hydraulicpump and the hydraulic motor is lowered due to amplification of theleakage loss of the hydraulic system resulted from an excessive flowrate and occurrence of the cavitation resulting from the loweredpressure and the excessively large flow rate on the low pressured side,and the like.

In addition, when a hydraulically driven car such as a fork lift truckrunning at a high speed is decelerated, a high pressure suddenly occursat the output side of the motor as if an emergency brake acts, andtherefore, is displaced by inertia. This is extraordinarily dangerous.Such and other many problems in the practical operation of such a carare as yet unsolved.

Briefly stated in accordance with one aspect of this invention, there isprovided a means for automatically preventing a motor, which ishydraulically driven by a pump and mechanicaily drives an inertial loadthrough a transmission shaft, from a pumping action of the motor causedby being driven by the inertial load, comprising blocking a reversepower transmission at the shaft. The blocking may be done by braking abrake disc fixed to the shaft or by declutching a pair of clutchingmembers arranged across the shaft. The automatic actuation of theblocking action may be either mechanically or electrcmagneticallyeffected.

The principal object of this invention is to provide a means forpreventing the hydraulic motor from pumping caused by being re erselydriven by the inertial load, or at least minimizing such an action.

Another object of this invention is to provide a means for preventingthe hydraulic power transmission system including the hydraulic motor, ahydraulic pump for driving the motor, and a prime mover for driving thepump, from any damage caused by the pumping action of the motor asabove.

Still another object of this invention is to provide a means forpreventing a car from being suddenly braked due to the pumping action asabove. The invention will be better understood and other objects andadditional advantages of the invention will become apparent upon perusalof the following description taken in connection with the drawings, inwhich:

FIG. l is a schematical axially sectional view of an embodiment of ahydraulic power transmission system in accordance with this invention;

FIG. 2 is a view similar to FIG. 1, but showing the second embodiment inaccordance with this invention;

PEG. 3 is another view still similar to FIG. 1, but showing the Thirdembodiment in accordance with this invention; and

FIG. 4 is still another view also similar to FIG. 1, but showing thefourth embodiment in accordance with this invention.

Similar numerals refer to similar parts throughout the several views.

Referring more particularly to the drawings, the preferred embodimentsof this invention will now be described; however, this description willbe understood to be illustrative of the invention and not as limiting itto the particular methods and constructions as shown and described.There is a hydraulic power transmission system including a prime mover(not shown), a variable capacity plate axial plunger pump 11, a plateaxial plunger motor 12, and an inertial load 25. The variable capacityplate axial plunger pump 11 is mechanically driven by the prime moverthrough a driving shaft. The plate axial plunger motor 12 ishydraulically driven by the plate axial plunger pump 11 through a pairof main conduits l3 and 14. The inertial load 25 is mechanically drivenby the plate axial plunger motor 12 through a shaft 35. The plate axialplunger pump 11 comprises a swash plate 15 which is controlled by meansof a controlling lever 16 swingably pivoted on a pivot 34 so as toincline the swash plate 15 in a well known manner.

EXAMPLE 1 Reference is now made to FIG. 1 illustrating the firstembodirnent of a hydraulic power transmission system in accordance withthis invention, in which the shaft 35 is provided with a brake disc 24arranged between a pair of hydraulic braking means 26 and 27, and fixedto the shaft 35 by means of a key 36. Each hydraulic braking means 26and 27 comprises a piston 23 adapted to be axially slidable in acylinder and loaded with a spring 21 pushing the piston 23 towards theworking chamber of the cylinder.

The controlling lever 16 swingably pivoted on the pivot 34 isarticulated also with a connecting rod for moving a spool containedinside a changeover valve 17 so that a pair of branched pipes 18 and 19branched from the pair of main conduits l3 and 14, respectively, arechanged over between two positions for communicating with a reservoir 33and for communicating with the working chamber of the cylinders of thehydraulic braking means 26 and 27. The communication with the reservoir33 as above serves for return and supply.

When the controlling lever 16 is inclined, the swash plate 15 ismechanically inclined thereby. The direction of rotation of the plateaxial plunger motor 12 depends upon the direction of the inclination.Provided that the main conduit 13 is the higher pressured side and themain conduit 14 is the lower pressure side for the proper drivingoperation of the plate axial plunger motor 12, in the event ofa reversedrive by the inertial load 25, the main conduit 14 becomes the higherpressure side and the main conduit 13 becomes the lower pressure side,although the direction of flow of the hydraulic medium is not changed.

In this embodiment, when the controlling lever 16 is not inclined, theplate axial plunger motor 12 is not actuated and, at the same time, thechangeover valve 17 interrupts all communications through the branchedpipes 18 and 19. When the controlling lever 16 is inclined, the spool ofthe changeover valve 17 is displaced for communicating either thebranched pipe 13 or 19 with a brake actuating pipe 20 leading to thechamber behind the pistons 23 inside the cylinders of the braking means26 and 27, and therefore, the hydraulic medium contained in the mainconduit 13 or 14, of which a higher pressure is produced by virtue ofthe reverse driving from the inertial load 25, is supplied to therecesses so as to push the pistons 23 against the action of the springs21 to push brake blocks fixed to the extremities of the piston rods ofthe pistons 23, respectively, against the brake disc 24 for deceleratingthe rotation of the shaft 35. When the high pressure is lowered to agiven value, the brake blocks are disengaged from the brake disc 24 byvirtue of the action of the springs 21 overcoming the hydraulic pressuresubjected to the pistons 23, so as to release the shaft 35.

EXAMPLE 2 Reference is now made to FIG. 2 illustrating the secondembodiment of a hydraulic power transmission system in accordance withthis invention, in which a changeover valve 28 corresponding to thechangeover valve 17 shown in FIG. 1 is provided and operatedelectromagnetically instead of hydraulically. When the controlling lever16 is operated, a switch 29 is adapted to be closed, so as to actuatethe changeover valve 28, which is adapted to operate quite similarly tothe preceding embodiment. A battery 30 and a main switch 31 are providedfor completing the circuit for electromagnetically changing over thevalve 28.

EXAMPLE 3 with and interrupted twice by a clutch 42, 43 and a slidejoint or spline joint 40 between the plate axial plunger motor 12 andthe inertial load 25. The controlling lever 16 arranged similarly to thefirst embodiment shown in FIG. 1 is adapted to operate a changeovervalve 17 which is adapted to supply the high-pressure hydraulic mediumto chambers of cylinders behind pistons 37 contained therein. A disc 41is fixed to the intermediate part of the shaft 35 and loaded by springs38 for biasing the disc 41 towards the plate axial plunger motor 12. Thesprings 38 are anchored to a frame 39 of the hydraulic clutching means.

When the controlling lever 16 is inclined so as to operate the plateaxial plunger motor 12, the changeover valve 17 is displaced so as tocommunicate either one of the main conduits i3 and 14 with the clutchingmeans actuating pipe 20. When an excessively high pressure occurs, thepistons 37 are actuated by the high-pressured hydraulic medium admittedinto the recesses behind the pistons 37 inside the cylinders, and pushedagainst the disc 41 against the action of the springs 38, and therefore,the intermediate part of the thrust shaft 35 is displaced towards theinertial load 25 by virtue of the slide joint 40, so that a driven disc43 of a clutch is disengaged from a driving disc 42 thereof, tointerrupt the reverse transmission of power from the inertial load 25 tothe plate axial plunger motor 12. When the main conduit i3 or 14 isreleased from the excessively high pressure of the hydraulic medium, thedriven disc 43 is again brought into engagement with the driving disc 42of the clutching means by virtue of the slide joint 46 and the action ofthe spring 38 so as to restore the power transmission from the plateaxial plunger motor 12 to the inertial load 25.

EXAMPLE 4 Reference is now made to FIG. 4 illustrating the fourthembodiment of a hydraulic power transmission system in accordance withthis invention, in which the second embodiment and the third embodimentof this invention are combined with each other. That is, the fourthembodiment comprises the controlling means similar to that of the secondembodiment and the clutching means similar to that of the thirdembodiment. More particularly, the controlling lever 16 cooperated witha switch 29 energizes the changeover valve 28 for communicating eitherone of the two main conduits 13 or 14 with the clutching means actuatingpipe 20. The pistons 37 are operated by an excessively high pressure ofthe hydraulic medium in either the main conduits 13 or 14 fordisengaging the driven disc 43 from the driving disc 42. When theexcessively high pressure of the hydraulic medium in the main conduits13 or 14 is restored, the driven disc 43 is again engaged with thedriving disc 42 by virtue of the slide joint 40 and by the action of thesprings 38 so as to transmit the power generated by the plate axialplunger motor 12 to the inertial load 25.

While particular embodiments of the invention have been illustrated anddescribed, modifications thereof will readily occur to those skilled inthe art. It should be understood th ere fore that the invention is notlimited to the particular methods and constructions disclosed but thatthe appended claims are intended to cover all modifications which do notdepart from the true spirit and scope of the invention. While a plateaxial plunger pump and a plate axial plunger motor have beenillustrated, any variable capacity hydraulic pump and/or any variablecapacity hydraulic motor may be substituted therefor, respectively.

I claim:

1. A means for automatically preventing a motor, which is hydraulicallydriven by a pump and mechanically drives an inertial load through atransmission shaft, from pumping caused by being driven by said inertialload, comprising a blocking means for blocking a reverse powertransmission from said inertial load to said motor through said shaft,at said shaft,

said blocking means including a plurality of brake elements and a brakedisc,

said brake disc being fixed to said shaft and arranged between saidbrake elements,

said brake elements being fixed to pistons inside cylinders,

respectively,

hydraulic means coacting with said pistons for automatically urging saidpistons hydraulically against said brake disc with a hydraulic mediumprovided for the power transmission, when an excessively high pressureoccurs in said medium as a result of said reverse power transmissionfrom said inertial load to said motor, and

a pair of main conduits for driving said motor by said pump,

and a changeover valve means coacting with said cylinders and mainconduits for automatically providing communication therebetween whensaid pump drives said motor.

2. The combination of claim 1 and wherein a mechanical means controlssaid changeover valve.

3. The combination of claim 1 and wherein an electromagnetic meanscontrol said changeover valve,

1. A means for automatically preventing a motor, which is hydraulicallydriven by a pump and mechanically drives an inertial load through atransmission shaft, from pumping caused by being driven by said inertialload, comprising a blocking means for blocking a reverse powertransmission from said inertial load to said motor through said shaft,at said shaft, said blocking means including a plurality of brakeelements and a brake disc, said brake disc being fixed to said shaft andarranged between said brake elements, said brake elements being fixed topistons inside cylinders, respectively, hydraulic means coacting withsaid pistons for automatically urging said pistons hydraulically againstsaid brake disc with a hydraulic medium provided for the powertransmission, when an excessively high pressure occurs in said medium asa result of said reverse power transmission from said inertial load tosaid motor, and a pair of main conduits for driving said motor by saidpump, and a changeover valve means coacting with said cylinders and mainconduits for automatically providing communication therebetween whensaid pump drives said motor.
 2. The combination of claim 1 and wherein amechanical means controls said changeover valve.
 3. The combination ofclaim 1 and wherein an electromagnetic means control said changeovervalve.